Circuits to control and drive brushless DC (BLDC) electric motors are known. In some arrangements, the circuits provide a particular a ramp-up of the speed of the electric motor when the electric motor is first powered up. However, such circuits are only able to provide one particular predetermined type of ramp-up.
Some known electric motor drive circuits are described in U.S. Pat. No. 7,590,334, issued Sep. 15, 2009, U.S. Pat. No. 7,747,146, issued Jun. 29, 2010, U.S. patent application Ser. No. 13/271,723, filed Oct. 12, 2011, U.S. patent application Ser. No. 13/599,225, filed Aug. 30, 2012, and U.S. patent application Ser. No. 13/599,234, filed Aug. 30, 2012, all of which are incorporated herein by reference in their entireties and assigned to the assignee of the present invention.
A BLDC electric motor can be used in different applications. For example, the same BLDC electric motor can be used with different fan blade arrangements in different applications. Different types of BLDC electric motors can also exhibit different load behaviors versus speed.
Motor noise, vibration, and efficiency are influenced by a variety of characteristics.
For sensor-less motor drive arrangements (i.e., motor drivers that do not rely upon Hall Effect elements to sense position of the motor shaft), reliable start-up is an important part of the design. Some sensor-less motor drive arrangements rely upon so-called “back EMF,” or simply “BEMF” generated on the motor windings to sense a position of a motor shaft. In order to sense the BEMF, the electric motor must be spinning at some minimum speed and drive signals to the electric motor must generally be turned off, and thus, BEMF is not conventionally used to sense motor position at the very beginning of a start-up of a motor.
Various methods have been used to start an electric motor. For example, a so-called “Trap Drive” arrangement has been used, in which motor windings of an electric motor are driven with trapezoidal (trap) drive signals through six states at a predetermined fixed rate during start-up. During start-up, in some embodiments, start-up motor current is controlled by pulse width modulation (PWM) of the trap drive signals, and in other embodiments, start-up motor current is controlled by current limiting of the trap drive signals. BEMF is checked during the start-up process and the commutation of the phases of the trap drive signals are synchronized with BEMF zero crossings.
After the electric motor is started with the above-described trap drive signals, in some embodiments, the motor control electronics continues to run the electronic motor with trap drive signals in a normal mode of operation.
One of the drawbacks of using the trap drive signals during start-up and/or during the normal mode of operation after start-up, is that the trap drive signals result in is audible noise from the electric motor due to vibrations. Even when the trap drive signals are used as an envelope for PWM drive signals with very low duty cycles and current levels, the noise can still be very prominent. For many applications, the noise is not acceptable.
Sine drives that result in sinusoidal currents in the motor windings are known. Sine drives are quieter than trap drives.
As described above, the BEMF signals are not available until the electric motor has achieved some minimum rotating speed. Thus, during start-up of the electric motor, a common method ramps up the motor slowly, without BEMF motor position information, and using a fixed and predetermined ramp-up rate and technique. However, different electric motors (e.g., motors with different inertial masses and coupled loads) require different motor drive signal start-up profiles.
A motor controller integrated circuit has only a limited number of pins. A motor controller integrated circuit must also be built for a low cost.
It would be desirable to provide a motor controller electronic circuit (either integrated or non-integrated) that uses a small number of pins, that is low cost (e.g., small silicon surface area), that can generate sine drive signals instead of trap drive signals for low noise, that can be used to drive a wide variety of types of electric motors, while providing a proper sine drive start-up profile synchronized with a sine drive normal mode of operation for each type of electric motor.